1. Field of the Invention
The present invention relates generally to the field of rehabilitation devices and, more specifically, to a cycle crank for use with patients with limited joint mobility.
2. Description of the Related Art
A number of rehab cycle cranks have been patented, but none with the particular combination of adjustability features of the present invention. Several examples are discussed below.
U.S. Pat. No. 935,495 (Grout, 1909) describes a variable throw cycle crank in which the length of the throw is variable by means of a cam-disk. The cam-disk causes the overall throw of the crank (measured as the distance between the pedal and the crank-shaft) to decrease on the up stroke and increase on the down stroke.
U.S. Pat. No. 4,606,241 (Fredriksson, 1986) provides an adjustable crank assembly comprising a hub assembly, a crank lever, a pivot arm, an adjustment member, a pedal, and an anchorage means for positioning the pedal on the pivot arm. A bearing arrangement is fixedly locked in any position along the adjustment member, and the anchorage is releasably locked into place on the pivot arm. By thus moving the position of the bearing arrangement on the adjustment member and the anchorage on the pivot arm, both the diameter of the cranking movement and the vertical position of the cranking movement can be adjusted.
U.S. Pat. No. 5,261,294 (Ticer et al., 1993) describes an adjustable elliptical crank mechanism which operates by means of a sleeve member that is disposed around a first shaft. The sleeve member is connected to a rotating arm, and an attachment means slides along the rotating arm. A first linkage means connects the first shaft and the attachment means, and a second linkage means connects first shaft and the sleeve member. The first and second linkage means allow the attachment means to selectively describe any of a range of circular or elliptical paths.
U.S. Pat. No. 5,573,481 (Piercy et al., 1996) describes a foot-operated therapeutic device in which the position of the pedal is adjustable relative to the pedal axis and the position of the pedal axis is adjustable relative to the saddle. By moving the pedal closer to the pedal axis, the diameter of rotation of the foot is reduced. By moving the pedal axis further away from the saddle, the device can accommodate a patient with a more limited range of motion.
U.S. Pat. No. 6,474,193 (Farney, 2002) and U.S. Pat. No. 6,820,517 (Farney, 2004) provide a pedal crank with a cam and a cam channel (much like the '495 patent discussed above), a hub fixed to the shaft of an exercise machine, and an arm that operates with a cam follower and a pair of rods. The arm includes the pedal of the exercise machine, and the cam follower extends into the channel of the cam. The pedal crank is extended on the down stroke to the maximum length of the rods and retracted on the upstroke, thereby alleviating some of the stress on the hip and knee joints.
U.S. Pat. No. 6,589,139 (Butterworth, 2003) describes a rehab cycle with a primary and a secondary crank that can be adjusted in relation to each other to allow for more passive movement on one side of the cycle and more dynamic movement on the other. Rotation of the secondary crank can be permitted or prevented relative to the primary crank, depending on the nature of disabilities or injuries of the user of the cycle.
U.S. Patent Application No. 2005/0020411 (Andrews) discloses a pedal stroke adjuster for cycles that selectively changes the diameter of the orbit traveled by the foot pedal to compensate for individuals with physical impairments that limit foot movement. A track member is secured to the cycle crank arm, and the pedal is fastened to a slider that is travelable to any of a plurality of different locations along the track member.
None of the above inventions possesses the combination of adjustability features and provides the smooth cadence afforded by the rehab crank of the present invention.